When wired correctly, green indicators on the IR2R and IR2S are always lit. Only when the door is open and theIR2R is receiving infrared from the sender does the IR2R’s amber indicator light. The HAL does not check the IR2wiring for errors. The IR2R’s green indicator flashes when the output is short-circuited. The amber indicator flasheswhen the signal is marginal, as for a dirty sensor, or if it’s too far away. The IR2 will operate with up to 5 feet (1.5meters) between sensors.NOTE: Distinguishing the IR2R from the IR2S: Both the send and receive IR parts have brown and bluewires, but the receiver also has a black wire.Expansion UnitsThis section provides an overview of available HAL Expansion Units. The original HAL1 has been discontinuedand is now a legacy system that includes a FireWire Expansion Bus and supports a single expansion unit type, theEXP1.Halogen version 3.0.0 introduced a new expansion bus, the HAL1x host, and a variety of new Expansion Unitsthat you can connect to the bus. This section explains both the old and the new expansion systems and the avail-able expansion units.WARNING! The two expansion systems are not compatible with each other. You cannot connect a newerexpansion unit (for example an EXP1x) to the older HAL1. Conversely, you cannot connect the older EXP1to the newer HAL1x. The “x” in the HAL1x name indicates interoperability with expansion units that alsohave an “x” in their name, such as the EXP1x, EXP3x, and EXP5x.CHAPTER 2: Hardware Component Details63